Medical apparatus system having optical fiber sensing capability

ABSTRACT

An apparatus and method for diagnosis or treatment of a vessel or organ. The apparatus includes a deformable body such as a catheter having a tissue ablation end effector and an irrigation channel in fluid communication therewith. At least two sensors are disposed within a distal extremity of the deformable body, the sensors being responsive to a wave in a specified range of frequency to detect deformations resulting from a contact force applied to the distal extremity. A microprocessor can be operatively coupled with the sensors to receive outputs therefrom, the microprocessor being configured to resolve a multi-dimensional force vector corresponding to the contact force. In one embodiment, the sensors are fiber Bragg grating sensors, and the wave is injected into the fiber Bragg grating strain sensors from a laser diode.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/11/436,926, filed May 15, 2006, which is acontinuation-in-part of U.S. patent application Ser. No. 11/237,053,filed Sep. 28, 2005, which claims the benefit of U.S. ProvisionalApplication No. 60/704,825, filed Aug. 1, 2005 and which also claimspriority from European Patent Application No. EP 05004852.9 filed Mar.4, 2005, all of which are hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to apparatus for exploring and treating anorgan that permits computation of a multi-dimensional force vectorresulting from contact between the distal extremity of the apparatus andthe tissue of the wall of the organ.

BACKGROUND OF THE INVENTION

For many years, exploration and treatment of various organs or vesselshas been possible using catheter-based diagnostic and treatment systems.Such catheters are introduced through a vessel leading to the cavity ofthe organ to be explored or treated or alternatively may be introduceddirectly through an incision made in the wall of the organ. In thismanner, the patient avoids the trauma and extended recuperation timestypically associated with open surgical procedures.

To provide effective diagnosis or therapy, it is frequently necessary tofirst map the zone to be treated with great precision. Such mapping maybe performed, for example, when it is desired to selectively ablatecurrent pathways within a heart to treat atrial fibrillation. Often, themapping procedure is complicated by difficulties in locating the zone(s)to be treated due to periodic movement of the heart throughout thecardiac cycle.

Previously-known systems for mapping the interior of a vessel or organare described, for example, in U.S. Pat. Nos. 6,546,271 and 6,226,542.The catheters described in those patents employ electromagnetic,magnetic or acoustic sensors to map the position of a distal end of thecatheter in space and then construct a three-dimensional visualizationof the vessel or organ interior.

One drawback of such previously known mapping systems is that they relyon manual feedback of the catheter and/or impedance measurements todetermine when the catheter is properly positioned in the vessel ororgan. Those systems do not measure contact forces with the vessel ororgan wall or detect contact forces applied by the catheter against theorgan or vessel wall that may modify the true wall location. Instead,previously known mapping methods are time-consuming, dependent upon theskill of the clinician, and cannot compensate for artifacts created byexcessive contact forces.

It therefore would be desirable to provide apparatus and methods fordetecting and monitoring contact forces between a mapping catheter andthe wall of the organ or vessel to permit faster and more accuratemapping. It also would be desirable to provide apparatus and methodsthat permit the process to be automated, thereby improving registrationof measured electro-physiologic values and spatial coordinates, forexample, by recording such values only where the contact forces fallwithin a predetermined range.

Once the topography of the vessel or organ is mapped, either the same ora different catheter may be employed to effect treatment. Depending uponthe specific treatment to be applied to the vessel or organ, thecatheter may comprise any of a number of end effectors, such as RFablation electrodes, a rotary cutting head, laser ablation system,injection needle or cryogenic fluid delivery system. Exemplary systemsare described, for example, in U.S. Pat. Nos. 6,120,520, 6,102,926,5,575,787, 5,409,000 and 5,423,807.

Because the effectiveness of such end effectors often depends having theend effector in contact with the tissue of the wall of the organ orvessel, many previously-known treatment systems include expandablebaskets or hooks that stabilize the distal extremity of the catheter incontact with the tissue. Such arrangements, however, may be inherentlyimprecise due to the motion of the organ or vessel. Moreover, thepreviously-known systems do not provide the ability of sense the loadapplied to the distal extremity of the catheter by movement of thetissue wall.

For example, in the case of a cardiac ablation system, at one extremethe creation of a gap between the end effector of the treatment systemand the tissue wall may render the treatment ineffective, andinadequately ablate the tissue zone. At the other extreme, if the endeffector of the catheter contacts the tissue wall with excessive force,if may inadvertently puncture the tissue, resulting in cardiactamponade.

In view of the foregoing, it would be desirable to provide acatheter-based diagnostic or treatment system that permits sensing ofthe load applied to the distal extremity of the catheter, includingperiodic loads arising from movement of the organ or tissue. It furtherwould be desirable to have a load sensing system coupled to controloperation of the end effector, so that the end effector is operated,either manually or automatically, only when the contact force isdetected to fall within a predetermined range.

U.S. Pat. No. 6,695,808 proposes several solutions to measure the forcevector arising from contact with the tissue surface, includingmechanical, capacitive, inductive and resistive pressure sensingdevices. One drawback of such devices, however, is that they arerelatively complex and must be sealed to prevent blood or other liquidsfrom disturbing the measurements. In addition, such load sensing devicesmay result in an increase in the insertion profile of the distalextremity of the catheter. Still further, sensors of the types describedin that patent may be subject to electromagnetic interference.

One previously-known solution for dealing with potential electromagneticinterference in the medical environment is to use light-based systemsrather than electrical measurement systems, such as described in U.S.Pat. No. 6,470,205 to Bosselman. That patent describes a robotic systemfor performing surgery comprising a series of rigid links coupled byarticulated joints. A plurality of Bragg gratings are disposed at thearticulated joints so that the bend angle of each joint may bedetermined optically, for example, by measuring the change in thewavelength of light reflected by the Bragg gratings using aninterferometer. Calculation of the bend angles does not requireknowledge of the characteristics of the rigid links.

International Publication No. WO 01/33165 to Bucholtz describes analternative spatial orientation system wherein wavelength changesmeasured in a triad of optical fiber strain sensors are used to computethe spatial orientation of a catheter or other medical instrument.Although the publication discloses that the strain sensors may beencased within a deformable sheath, as in Bosselman, calculation of thebend angles is not described as requiring characterization of thematerial properties of the deformable sheath.

Accordingly, it would be desirable to provide diagnostic and treatmentapparatus, such as a catheter or guide wire, that permits sensing ofloads applied to a distal extremity of the apparatus, but which do notsubstantially increase the insertion profile of the apparatus.

It further would be desirable to provide diagnostic and treatmentapparatus, such as a catheter and guide wire, that permits computationof forces applied to a distal extremity of the apparatus, and which aresubstantially immune to electromagnetic interference.

It still further would be desirable to provide a diagnostic andtreatment apparatus, such as catheter system, that permits computationof forces applied to a distal extremity of the catheter that issubstantially immune to environmental conditions encountered during useof the catheter, such as exposure to body fluids and the presence ofroom-to-body temperature gradients.

SUMMARY OF THE INVENTION

In view of the foregoing, it is object of the present invention toprovide diagnostic or treatment apparatus that permits sensing of theload applied to a distal extremity of apparatus, including periodicloads arising from movement of the organ or tissue.

It is another object of this invention to provide apparatus and methodsfor detecting and monitoring contact forces between an interventionalapparatus, such as a mapping catheter or guide wire, and the wall of theorgan or vessel to facilitate the speed and accuracy of such mapping.

It is a further object of the present invention to provide apparatus andmethods that enable a mapping or treatment process to be automated,thereby improving registration of measured electro-physiologic valuesand spatial coordinates, for example, by recording such values onlywhere the contact forces fall within a predetermined range.

It is also an object of this invention to provide apparatus wherein aload sensing system is coupled to control operation of an end effectorof a diagnostic or treatment apparatus, so that the end effector isoperated, either manually or automatically, only when the contact forceis detected to fall within a predetermined range.

It is another object of this invention to provide diagnostic andtreatment apparatus, that permit sensing of loads applied to a distalextremity of the apparatus, but which do not substantially increase theinsertion profile of the apparatus.

It is a further object of this invention to provide diagnostic andtreatment apparatus that permit computation of forces applied to adistal extremity of the apparatus, and which are substantially immune toelectromagnetic interference.

It is still another object of this invention to provide a diagnostic andtreatment apparatus that permits computation of forces applied to adistal extremity of the catheter, but which is substantially immune toenvironmental conditions encountered during use of the catheter, such asexposure to body fluids and the presence of room-to-body temperaturegradients.

It is also an object of this invention to provide apparatus for use in ahollow-body organ, such as the heart, that permits sensing of loadsapplied to a distal extremity of the apparatus during movement of theorgan, so as to optimize operation of an end effector disposed withinthe distal extremity.

These and other objects of the invention are accomplished by providingmedical apparatus, such as catheter, having at least two optical fibersensors disposed in a distal extremity configured to deform responsiveto contact forces, and processing logic programmed to compute at least atwo-dimensional force vector responsive to detected changes in theoptical characteristics of the optical fiber sensors. The apparatus ofthe present invention may be configured as a catheter or guide wire, ormay be employed in other medical apparatus where knowledge of tissuecontact forces is desired.

More preferably, the apparatus of the present invention comprises threeoptical fiber sensors disposed within the distal extremity so that theyare not co-planar. For example, the three optical fiber sensors may bearranged at the apices of an equilateral triangle centered on thegeometric axis of the apparatus, although other configurations also maybe employed. Use of three such optical fiber sensors advantageouslypermits the computation of a three-dimensional force vector. The opticalfiber sensors preferably are chosen from among a Fiber Bragg Grating(FBG), an Intrinsic Fabry-Perot Interferometer (IFPI), an ExtrinsicFabry-Perot Interferometer (EFPI), a Long Period Grating (LPG), a two,three or four arm Michelson interferometer (MI), a Brillouin scatteringstrain sensor, or intensity-based fiber optic strain sensor.

Further in accordance with the principles of the present invention, theapparatus includes processing logic, such as programmed general purposemicroprocessor or application specific integrated circuit, operativelycoupled to receive an output signal from the optical fiber sensors, andto compute a two- or three-dimensional force vector from that outputsignal, depending upon the number of optical fiber sensors employed. Theprocessing logic may be programmed with a matrix of values associatedwith physical properties of an individual device, and applies thosevalues to the detected changes in wavelength to compute the externalforces applied to the distal extremity. More preferably, a force-strainconversion matrix specific for each device is determined duringmanufacture, and that force-strain conversion is associated with thedevice via an appropriate memory device, label or tag.

In accordance with the one aspect of the present invention, two opticalfiber sensors may be used provided that the neutral axis of the distalextremity of the apparatus is well characterized. More preferably, threeoptical fiber sensors are disposed within the distal extremity to allowdeformations (elongation or contraction) imposed on the deformable bodyto be measured at three or more non-planar points.

The extremely small dimensions of the optical fiber sensors provideample space in the distal extremity of the apparatus to house for otherdiagnostic or treatment devices. When configured as a catheter or guidewire, the device has a substantially reduced insertion profile relativeto previously-known systems having force-sensing capability. Inaddition, the optical nature of the sensors ensures that the possiblepresence of liquids does not disturb the measurements, and ensures ahigh degree of immunity from electromagnetic interference.

The apparatus of the present invention optionally may include any of anumber of previously-known end effectors disposed in the distalextremity for treating a vessel or organ, for example, an electrode tomeasure an electric potential (e.g., to perform an endocavityelectrocardiogram), an electrode configured to ablate tissue bydeposition of radiofrequency energy, an irrigation channel, and/or athree-dimensional positioning sensor.

Advantageously, the load sensing system of the present invention may beemployed to continuously monitor deflection of a distal extremity. Forexample, the signal output by the load sensing system may be used toguide or control the use and operation of an end effector of a cathetereither manually or automatically. Illustratively, when employed as partof an electrophysiology mapping catheter, the present invention permitselectrical potentials of the tissue to be measured only at contactpositions where the contact force applied to the distal extremity of thecatheter by the tissue wall falls within a predetermined range. Such anarrangement not only offers to improve spatial registration between themapped values and tissue location, but also makes possible the use ofrobotic systems capable of automating the mapping process. As a furtherexample, the output of the load sensing system may be used to controloperation of a treatment end effector, for example, to position the endeffector in contact with the organ wall and to energize the ablationelectrode only when the contact force is detected to fall within apredetermined range.

In addition, the distal part of at least one of the optical fibers, oran additional optical fiber, extends beyond the others and is equippedwith an additional FBG, LPG, IFPI, EFPI or Brillouin scattering typesensor to permit the temperature of the distal extremity to bemonitored.

Alternatively, or in addition, a temperature sensor may be disposed inthe distal extremity in close proximity to the optical fiber sensors.Temperatures measured by the temperature sensor may be used tocompensate for deformations of the deformable body arising fromtemperature variations, which might otherwise erroneously be interpretedas force-related deformations. The temperature sensor may comprise anyof a number of temperature sensors. More specifically, the temperaturesensor comprises an additional optic fiber that is not constrained todeform in unison with the distal extremity, but instead is free toexpand due to temperature variations. In a preferred embodiment, thetemperature sensor comprises an additional FBG, LPG, IFPI, EFPI orBrillouin scattering type optical fiber sensor.

The additional optical fiber also could extend beyond the other opticalfibers and include an additional FBG, LPG, IFPI, EFPI or Brillouinscattering type sensor to measure the temperature of the distalextremity. Alternatively, the distal part of the additional fiberextends beyond the other optical fibers in the distal extremity andincludes a temperature sensor comprising a Michelson interferometersensor or an intensity sensor.

In accordance with a preferred alternative embodiment, the apparatus maycomprise an electrophysiology catheter comprising an elongated portion,a distal extremity, and a proximal end. An irrigation tube extends fromthe proximal end to the distal extremity and has a plurality of opticalfibers arranged symmetrically around its circumference. The opticalfibers include sensors, such as Bragg Gratings, disposed near the distalextremity. In accordance with one aspect of the invention, theirrigation tube in the vicinity of the distal extremity comprises aflexible tube having a low thermal expansion coefficient which reducessensor artifacts introduced by environmental effects, such a temperaturefluctuations.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention, its nature and various advantageswill be more apparent from the accompanying drawings and the followingdetailed description of the preferred embodiments, in which:

FIG. 1 is a schematic view of apparatus according to the invention;

FIG. 2 is a schematic plan view of the distal extremity of FIG. 1;

FIG. 3 is a section according to III-III of FIG. 2;

FIG. 4 is a schematic view of the side of the distal extremity showingthe disposition of the Fiber Bragg Grating (FBG) or Long Period Grating(LPG) sensors;

FIG. 5 is a schematic view of the side of the distal extremity showingthe disposition of the Intrinsic Fabry-Perot Interferometer (IFPI)sensors;

FIG. 6 is a schematic view of the side of the distal extremity showingthe disposition of the Extrinsic Fabry-Perot Interferometer (EFPI)sensors;

FIG. 7 is a schematic view of the side of the distal extremity showingthe disposition of the Michelson interferometer sensors;

FIG. 8 is a schematic view of the side of the distal extremity showingthe disposition of the High Resolution Brillouin sensors;

FIG. 9 is a schematic view of the side of the distal extremity showingthe disposition of the reflection intensity sensors;

FIG. 10 is a schematic view of the side of the distal extremity showingthe disposition of the microbending intensity sensors;

FIG. 11 is a perspective view of three optical fibers in contact witheach other;

FIG. 12 is a perspective view of three optical fibers in contact witheach other and forming an integral part;

FIG. 13 is a schematic plan view of the distal extremity with theoptical fibers of FIG. 6 forming an integral part of the distalextremity;

FIG. 14 is an exploded perspective view of the distal extremity of anexemplary catheter constructed in accordance with the present invention;

FIG. 15 is a schematic plan view of the distal extremity including afourth optical fiber;

FIG. 16 is a schematic view of apparatus of the present inventionwherein the output of the load sensing system is utilized to controlautomated operation of the apparatus;

FIG. 17 is a schematic view of an alternative embodiment of apparatus ofthe present application;

FIG. 18 is a perspective view of a distal subassembly of the apparatusof FIG. 17;

FIG. 19 is a perspective view of the distal subassembly of FIG. 18including a protective housing, which is partially cut-away;

FIG. 20 is a cross-sectional view of the distal subassembly of FIG. 19taken along line 20-20; and

FIG. 21 is a perspective view of an exemplary deflectable catheter shaftfor use with the distal subassembly of FIG. 19.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention is directed to medical apparatus and methods foruse with diagnostic and treatment systems wherein it is desired tomeasure contact forces between a distal extremity of the apparatus and atissue wall of an organ or vessel. The load sensing capability of thepresent invention may be used intermittently to measure the contactforces at discrete points, or alternatively, used to continuouslymonitor contact forces to assist in manipulation and operation of theapparatus.

Medical apparatus incorporating the present invention illustratively maybe configured as catheters or guide wires to be manually manipulated bya clinician, with the clinician using a visual or audio cue output bythe load sensing system to determine, for example, optimum position formeasuring an electrophysiologic value or performing treatment.Alternatively, the medical apparatus may be robotically controlled, withthe load sensing system of the present invention providing a feedbackand control system.

Advantageously, medical apparatus equipped with the load sensing systemof the present invention are expected to permit faster, more accuratediagnosis or treatment of a vessel of organ, with improved registrationbetween measured values and spatial locations. For example, a catheterwith the inventive load sensing system would permit mapping of cardiacelectrical potentials by providing reproducible contact forces betweenthe distal extremity of the catheter and the tissue wall, thereby makingthe results of the mapping process less dependent on the skill of theindividual clinician and facilitating automated procedures.

Referring now to FIGS. 1 and 2, exemplary apparatus constructed inaccordance with the principles of the present invention comprisescatheter 1 having proximal end 2 coupled to console 3 via cable 4. Asdescribed in detail below, catheter 1 includes distal extremity 5 thatillustratively carries any one or more of a number of end effectorsknown in the art for diagnosing or treating a vessel or organ. While thepresent invention is described in the context of a catheter system forcardiac mapping and ablation, it will be understood that medicalapparatus constructed in accordance with the present inventionadvantageously may be used for other purposes, such as delivering drugsor bioactive agents to a vessel or organ wall or performingtransmyocardial revascularization or cryo-ablation, such as described inthe above-referenced patents.

Proximal end 2 preferably includes storage device 2 a, such as a memorychip, RFID tag or bar code label, which stores data that may be used incomputing a multi-dimensional force vector, as described herein after.Alternatively, storage device 2 a need not be affixed to proximal end 2,but instead could be a separate item, e.g., packaging, individuallyassociated with each catheter. Proximal end 2 may be manipulatedmanually or automatically to cause a desired amount of articulation orflexion of distal extremity 5 using mechanisms which are per se known inthe art, such as pull wires or suitably configured electroactivepolymers. Catheter 1 also may be advanced, retracted and turned manuallyor automatically.

Distal extremity 5 of catheter 1 comprises a deformable body having atleast two optical fiber sensors that extend proximally and are coupledto console 3 via proximal end 2 and cable 4. More preferably, catheter 1includes three optical fiber sensors disposed therein. In addition,control signals to and from the end effector(s) in distal extremity 5are transmitted via suitable components of cable 4 to console 3, to atactile component of proximal end 2. As will be apparent, the nature ofcable 4 depends on the nature of the end effectors disposed in distalextremity 5 of catheter 1.

Console 3 comprises electronic and optical components to drive theoptical fiber sensors and to interpret the output signals therefrom.Console 3 further includes processing logic 6, such as a programmedgeneral purpose microprocessor or application-specific integratedcircuit, which receives an output signal corresponding to wavelengthchanges manifested in the optical fiber sensors due to forces applied tothe distal extremity of the deformable body. Processing logic 6 computesa multi-dimensional force vector based upon that output signal and amatrix of physical characteristics of the individual deformable body, asdescribed in detail below. Console 3 preferably also includes means tomanifest an output from the load sensing system, such as a visualdisplay or an auditory device. Alternatively, console 3 may output asignal for display on a separate monitor.

Referring now to FIGS. 2 and 3, catheter 1 preferably has at least twooptical fiber sensors 7 disposed within it, so that deformation ofdistal extremity 5 is transferred to the sensors 7. Two optical fibersensors may be employed so long as the location of the neutral axis ofthe distal extremity is known or determined during manufacture. Morepreferably, distal extremity 1 includes at least three optical fibersensors, and comprises a molded, machined or extruded material, such astypically are used in making guide wires or catheters. To ensure thatthe optical fibers form an integral part of catheter 1, the opticalfibers may be affixed within the distal extremity using adhesive orother means as, for example, overmolding or co-extrusion. In FIG. 3,optical fibers 7 are glued into distal extremity 5 using adhesive 8.

Preferably, catheter 1 comprises a liquid crystal polymer (“LCP”) thathas a small positive or even negative coefficient of thermal expansionin the direction of extrusion. A variety of liquid crystal polymers areknown in the art and such materials may be coated with parylene or ametallic coating to enhance resistance to fluid absorption.

Where three optical fiber sensors are employed, optical fibers 7 aredisposed in distal extremity 5 so that the optical fiber sensors are notco-planar, i.e., are not situated in a single plane. Illustratively, theoptical fibers are disposed at the apices of an equilateral trianglecentered on the longitudinal axis of the catheter. Other configurationsare possible, so long as optical fibers experience different degrees ofbending and elongation during deformation of distal extremity 5. Opticalfiber sensors 7 may be chosen from among a Fiber Bragg Grating (FBG), aLong Period Grating (LPG), an Intrinsic Fabry-Perot Interferometer(IFPI), an Extrinsic Fabry-Perot Interferometer (EFPI), a two, three orfour arm Michelson interferometer (MI), a Brillouin scattering strainsensor, or intensity-based fiber optic strain sensor.

Referring now to FIG. 4, catheter 1 is depicted housing three opticalfibers 7 having FBG or LPG strain sensors 9 disposed in distal extremity5. An FBG sensor is an interferometer in which a stable Bragg grating ispermanently impressed (e.g., photo-etched) into the core of the fiber.The region of periodic variation in the index of refraction of the fibercore acts as a very narrowband reflection filter that reflects lighthaving a predetermined Bragg wavelength. Light therefore is reflectedfrom the FBG in a narrow spike with a center wavelength that is linearlydependent on the Bragg wavelength and the mean index of refraction ofthe core. Consequently, deformations that alter the gratingcharacteristics result in a shift in the reflected Bragg wavelength.

An LPG is similar in construction to an FBG, and comprises a single modefiber having periodic index modulation of the refractive index of thefiber core with a much longer period than an FBG. Use and operation of acatheter employing LPGs rather than FBGs is similar to that describedbelow.

During use of the apparatus, the distal extremity of catheter 1 iscompressed and bent due to loads imposed by contacting the tissue of theorgan. The portions of optical fibers 7 that are situated in the distalextremity also are deformed but in a varying degrees according to theirrespective positions in the distal extremity. In addition, the distalextremity may be deflected by deflecting a more proximal portion of thecatheter using any of a variety of previously-known catheter deflectionmechanisms, such as described in U.S. Pat. No. 4,960,134 to Webster,which is incorporated herein by reference. In this case, the apparatuswill compute the force with which the distal extremity contacts thetissue of the organ or vessel.

The initial calibration of the FBG sensors, i.e., the average wavelengthreflected from the Bragg grating in the absence of any applied forces(referred to as the “Bragg wavelength”) is determined from gratingcharacteristics impressed during manufacture of the optical fiber. Anydeviations from the Bragg wavelength are proportionately related to anexact parameter, such as strain. In the embodiment of FIG. 4, the Bragggrating allows the deformation (elongation or contraction) of each ofoptical fibers 7 to be quantified by measuring the change in wavelengthof the light reflected by the Bragg grating.

The foregoing information, together with known physical properties ofthe distal extremity of the catheter, enable processing logic 6 ofconsole 3 to calculate the components of a multidimensional force vectorwith appropriate algorithms. The force vector then may be displayed orotherwise manifested, for example, as a graphic on a display screen orby varying the pitch emitted from an auditory device housed in orassociated with console 3.

Still referring to FIG. 4, one of optical fibers 7 preferably extendsbeyond the others and includes second FBG (or LPG) 10 for measuring thetemperature of the front end of the distal extremity. Temperaturechanges at the front end of the distal extremity may arise, e.g., due tooperation of an ablation electrode, and will cause a change in theassociated Bragg wavelength. By knowing the physical properties of thefiber and measuring the wavelength of the light reflected by thegrating, processing logic 6 may compute the temperature at the level ofthe distal extremity, for example, to monitor tissue ablation progress.

Referring again to FIG. 1, console 3 comprises a laser, preferably atunable laser diode, arranged to inject a beam of light into the opticalfibers through cable 4, and a photodetector that detects variations inthe characteristics of the reflected light beam due to deformationsimposed on the strain sensors and distal extremity 5. Preferably,console 3 includes a Fiber Bragg Grating Demodulator.

In such a system, each of the optical fiber sensors has a Bragg gratingwith a different wavelength, and which therefore responds in a specifiedrange of frequency. A tunable laser is coupled to all of the opticalfiber sensors and scans a certain frequency several times per second. Aphotodiode records the wavelength change for each Bragg grating when thefrequency of the laser centers on the grating frequency. In this manner,each of the optical fiber sensors may be interrogated as the tunablelaser scans through the grating frequencies of the sensors.

Further in accordance with the principles of the present invention,processing logic 6 is programmed to compute a two- or three-dimensionalforce vector from the output of the Fiber Bragg Grating Demodulator. Thetheory underlying these computations is now described.

For apparatus having three fiber optic Bragg strain sensors embeddedwithin the distal extremity of the catheter, the total strain may becomputed using:

$\begin{matrix}{\begin{bmatrix}ɛ_{1,t} \\ɛ_{2,t} \\ɛ_{3,t} \\{\Delta\; T_{t}}\end{bmatrix} = {\begin{bmatrix}C_{ɛ} & 0 & 0 & C_{ɛ\; T} \\0 & C_{ɛ} & 0 & C_{ɛ\; T} \\0 & 0 & C_{ɛ} & C_{ɛ\; T} \\0 & 0 & 0 & C_{T}\end{bmatrix} \cdot \left( {\begin{bmatrix}\lambda_{1,t} \\\lambda_{2,t} \\\lambda_{3,t} \\\lambda_{4,t}\end{bmatrix} - \begin{bmatrix}\lambda_{1,r} \\\lambda_{2,r} \\\lambda_{3,r} \\\lambda_{4,r}\end{bmatrix}} \right)}} & (1.1) \\{ɛ_{t} = {C \cdot \left( {\lambda_{t} - \lambda_{r}} \right)}} & \left( {1.1a} \right)\end{matrix}$

Where: r—time when reference (zero) measurement is set

-   -   t—time relative to reference time    -   λ_(i,r), i=1,4—reference wavelengths of Bragg-gratings    -   λ_(i,t), i=1,4—wavelengths of Bragg-gratings at time t    -   ε_(i,t), i=1,3—total strain values at time t    -   ΔT_(t)—Temperature change at time t    -   C_(ε)—coefficient of linearity between the wavelength and strain    -   C_(ε) _(T) —coefficient of temperature compensation of the        Bragg-grating    -   C_(T)—coefficient of linearity between the wavelength and        temperature        -   λ_(r)—Matrix (vector) of Bragg-gratings reference            wavelengths        -   λ_(t)—Matrix (vector) of Bragg-gratings wavelengths at time            t        -   ε_(t)—Matrix (vector) of total strain and temperature            changes        -   C—Strain transducer and compensation matrix

The total strain includes a component due to thermal expansion of thedistal extremity arising from the difference between the measuredtemperature of the distal extremity and a predetermined referencetemperature. The elastic strain, which is a function of the appliedforce, therefore may be calculated using:

$\begin{matrix}{\begin{bmatrix}ɛ_{{{el}\; 1},t} \\ɛ_{{{el}\; 2},t} \\ɛ_{{{el}\; 3},t}\end{bmatrix} = {\left\lbrack \left| \begin{matrix}1 & 0 & 0 & {- \alpha_{Tc}} \\0 & 1 & 0 & {- \alpha_{Tc}} \\0 & 0 & 1 & {- \alpha_{Tc}}\end{matrix} \right. \right\rbrack \cdot \begin{bmatrix}ɛ_{1,t} \\ɛ_{2,t} \\ɛ_{3,t} \\{\Delta\; T_{t}}\end{bmatrix}}} & (1.2) \\{ɛ_{{el},t} = {\alpha_{T} \cdot ɛ_{t}}} & \left( {1.2a} \right)\end{matrix}$

Where: ε_(eli,t), i=1,3—elastic strain values at time t

-   -   α_(T)—Thermal expansion coefficient of catheter material (PEEK)        -   ε_(el,t)—Matrix (vector) of elastic strain at time t        -   α_(T)—Temperature reduction matrix            (1.1a)^(1.2a)            ε_(el,t)=α_(T) ·C·(λ_(t)−λ_(r))  (1.3)

The elastic strains are related to the internal forces experienced bythe optical fiber sensors as a function of both the physical dimensionsof, and the material properties of, the distal extremity:

$\begin{matrix}{\begin{bmatrix}ɛ_{{{el}\; 1},t} \\ɛ_{{{el}\; 2},t} \\ɛ_{{{el}\; 3},t}\end{bmatrix} = {\begin{bmatrix}1 & y_{1} & {- x_{1}} \\1 & y_{2} & {- x_{2}} \\1 & y_{3} & {- x_{3}}\end{bmatrix} \cdot \begin{bmatrix}\frac{1}{E_{ten} \cdot A} & 0 & 0 \\0 & \frac{1}{E_{flex} \cdot I_{x}} & 0 \\0 & 0 & \frac{1}{E_{flex} \cdot I_{y}}\end{bmatrix} \cdot \begin{bmatrix}N_{z,t} \\M_{x,t} \\M_{y,t}\end{bmatrix}}} & (2.1) \\{ɛ_{{eI},t} = {G \cdot \delta \cdot I_{F,t}}} & \left( {2.1a} \right)\end{matrix}$

-   -   Where: x_(i) and y_(i), i−1,3—coordinates of Bragg-gratings with        respect to center of gravity of the catheter cross-section        -   E_(ten)—Equivalent tension/compression Young modulus of            catheter        -   E_(flex)—Equivalent flexural Young modulus of catheter        -   I_(x)—Moment of inertia with respect to x axis        -   I_(y)—Moment of inertia with respect to y axis        -   N_(z,t)—Normal force in direction of z axis at time t        -   M_(x,t)—Bending moment with respect to x axis at time t        -   M_(y,t)—Bending moment with respect to y axis at time t            -   G—Geometry matrix            -   δ—Matrix of flexibility            -   I_(F,t)—Matrix (vector) of internal forces at time t

Equation (2.1) may be rearranged to solve for the internal forces as afunction of the elastic strain. The elastic strain from equation (1.3)may then be substituted into the rearranged matrix system to compute theinternal forces as a function of the elastic strain, as shown inEquation (2.3) below:

$\begin{matrix}{\left. (2.1)\Rightarrow\begin{bmatrix}N_{z,t} \\M_{x,t} \\M_{y,t}\end{bmatrix} \right. = {\quad{\left. {{\begin{bmatrix}{E_{ten} \cdot A} & 0 & 0 \\0 & {E_{flex} \cdot I_{y}} & 0 \\0 & 0 & {E_{flex} \cdot I_{y}}\end{bmatrix} \cdot \begin{bmatrix}1 & y_{1} & {- y_{1}} \\1 & y_{2} & {- x_{2}} \\1 & y_{3} & {- x_{3}}\end{bmatrix}^{- 1} \cdot \begin{bmatrix}ɛ_{{{eI}\; 1},t} \\ɛ_{{{eI}\; 2},t} \\ɛ_{{{eI}\; 3},t}\end{bmatrix}}\left( {2.1a} \right)}\Rightarrow I_{F,t} \right. = {S \cdot G^{- 1} \cdot ɛ_{{eI},t}}}}} & (2.2)\end{matrix}$

Where: S=δ⁻¹—Stiffness matrix(1.3)^(2.1a)

I _(F,t) =S·G ⁻¹·α_(T) ·C·(λ_(t)−λ_(r))  (2.3)

It remains only to relate the internal forces experienced by the opticalfiber sensors to the external contact forces actually exerted on thedistal extremity by the tissue wall. These forces are computed based onthe positions of the optical fiber sensors from the exterior wall of thedistal extremity, assuming the catheter material is substantiallyincompressible:

$\begin{matrix}{\begin{bmatrix}F_{x,t} \\F_{y,t} \\F_{z,t}\end{bmatrix} = {\begin{bmatrix}0 & 0 & {- \frac{1}{d}} \\0 & \frac{1}{d} & 0 \\{- 1} & 0 & 0\end{bmatrix} \cdot \begin{bmatrix}N_{z,t} \\M_{x,t} \\M_{y,t}\end{bmatrix}}} & (3.1) \\{F_{t} = {d \cdot I_{F,t}}} & \left( {3.1a} \right)\end{matrix}$

-   -   Where: F_(x,t)—Touching external transversal force at time t, in        direction of x axis (with opposite sense)        -   F_(y,t)—Touching external transversal force at time t, in            direction of y axis (with opposite sense)        -   F_(z,t)—Touching external normal force at time t, in            direction of z axis (with opposite sense, compression is            positive)        -   d—distance between the touching point of lateral forces and            the cross-section with sensors (along z axis)            -   F_(t)—Matrix of touching external forces at time t            -   d—Matrix of conversion                (2.3)^(3.1a)                F _(t) =d·S·G ⁻¹·α_(T) ·C·(λ_(t)−λ_(r))  (3.2)                F _(t) =K _(λ)·(λ_(t)−λ_(r))=K _(λ)·λ_(t) −F _(r)  (3.3)    -   Where: K_(λ)—Force transducer matrix,        K _(λ) =d·S·G ⁻¹·α_(T) ·C  (3.4)        -   F_(r)— Reference force matrix (vector),            F _(r) =K _(λ)·λ_(t)  (3.5)

Solution of equations (3.1) to (3.5) provides the normal and transverseforces applied to the external surface of the deformable body, i.e.,F_(norm,t)=F_(z,t) and F_(trans,t)=square root (F² _(x,t)+F² _(y,t)).The angle γ_(t) of application of the transverse force may be computedfrom Table I:

TABLE I F_(x,t) F_(y,t) γ_(t) ≧0 ≧0 arcsin(F_(y,t)/F_(tran,t)) <0 ≧0 Π −arcsin(F_(y,t)/F_(tran,t)) <0 <0 Π − arcsin(F_(y,t)/F_(tran,t)) ≧0 <02 * Π + arcsin(F_(y,t)/F_(tran,t))

Many of the values employed in equations (1.1) to (3.5) are related tothe material properties of the distal extremity or optical fibersensors, such as the Bragg wavelengths, thermal expansion coefficientsand elastic moduli. Other values, such as the distances between theoptical fiber sensors and the external surface of the distal extremitymay be subject to variations as a consequence of the manufacturingprocess employed.

To ensure the accuracy of the computed force vector, specificinformation for each catheter may be stored in storage device 2 a.Generally, the information make take the form of a data file that isinput to console 3 prior to use of the catheter. For example, storagedevice 2 a may comprise a memory chip associated with cable 4 in whichsuch information is stored, or a bar code or a RFID tag located onproximal end 2 of the catheter or the packaging for the catheter.Alternatively, data specific to an individual catheter may be uploadedto console 3 from an item of removable storage (e.g., CD) or via securedownload from the manufacturer's website.

The information specific to each catheter may be obtained during acalibration step, conducted during manufacture of the catheter, bysubjecting the distal extremity of the catheter to a series of knownforces. In this case, the foregoing equations may be collapsed so thenormal and transverse forces may be computed directly from aforce-to-wavelength conversion matrix:F(t)=K(λ(t)−λ₀)  (4.0)where:

F(t) is the vector of forces [F_(x,t), F_(y,t), F_(z,t)],

λ(t) is the vector of wavelengths a [λ_(1,t), λ_(2,t), λ_(3,t)] measuredfor the individual sensors,

λ₀ is the vector of wavelengths [λ⁰ ₁, λ⁰ ₂, λ⁰ ₃] measured for theindividual sensors with zero applied force, and

K is a matrix computed when the deformable body is subjected to theseries of known forces.

During the calibration step of manufacture, the catheter is subjected tothe following forces in series: (1) a purely axial force of knownmagnitude F′; (2) a lateral force of known magnitude F″; and (3) alateral force of known magnitude F′″ applied 90 degrees to theorientation of force F″. When all of the forces F′, F″, F′″ andwavelengths are known, the force-to-strain conversion matrix K may becomputed as:K=F(λ(t)−λ₀)⁻¹  (5.0)or:

$\begin{matrix}{{\begin{bmatrix}F_{x} & F_{x}^{\prime} & F_{x}^{''} \\F_{y} & F_{y}^{\prime} & F_{y}^{''} \\F_{z} & F_{z}^{\prime} & F_{z}^{''}\end{bmatrix}\begin{bmatrix}\left( {\lambda_{1} - \lambda_{1}^{0}} \right) & \left( {\lambda_{1}^{\prime} - \lambda_{1}^{0}} \right) & \left( {\lambda_{1}^{''} - \lambda_{1}^{0}} \right) \\\left( {\lambda_{2} - \lambda_{2}^{0}} \right) & \left( {\lambda_{2}^{\prime} - \lambda_{2}^{0}} \right) & \left( {\lambda_{2}^{''} - \lambda_{2}^{0}} \right) \\\left( {\lambda_{3} - \lambda_{3}^{0}} \right) & \left( {\lambda_{3}^{\prime} - \lambda_{3}^{0}} \right) & \left( {\lambda_{3}^{''} - \lambda_{3}^{0}} \right)\end{bmatrix}}^{- 1} = {\quad\begin{bmatrix}a_{11} & a_{12} & a_{13} \\a_{21} & a_{22} & a_{23} \\a_{31} & a_{32} & a_{33}\end{bmatrix}}} & (5.1)\end{matrix}$

Force-to-strain conversion matrix K then may be stored in storage device2 a associated with the corresponding device, as described herein above.The values of the force-to-conversion matrix then may be input toconsole 3 when the catheter is coupled to the console using a bar codereader, input pad or direct electrical connection through cable 4. Oncematrix K is provided for a given distal extremity, the normal force,transverse force and angle of application of the transverse force may becomputed as described above and using Table I.

The values for the normal force, transverse force and angle ofapplication of the transverse force, computed as described above, may beoutput as numerical values to a display monitor that forms part ofconsole 3 or which is associated with console 3. In addition, a graphicincluding a variable size or colored arrow may be displayed pointing ata position on the circumference of a circle to visualize the magnitudeand direction of the transverse force applied to the distal extremity.By monitoring this display, the operator may continuously obtainfeedback concerning the contact forces applied to the distal extremityof the catheter.

Referring now to FIG. 5, an alternative embodiment is described in whichoptical fiber strain sensors 7 comprise Intrinsic Fabry-PerotInterferometers (IFPI). One of the optical fibers is extended andcomprises a second IFPI sensor 13 for measuring the temperature of thefront end of the distal extremity.

An IFPI comprises a single mode optical fiber having segment havingreflectors 12 disposed at either end to define optical cavity 11. Thereflectors may comprise semi-reflective mirror surfaces formed in thefiber, or alternatively may comprise two FBGs. Light emitted from alaser diode disposed in console 3 impinges upon the proximal reflectorand is partially reflected back at specific wavelengths 14. Lightpassing through the proximal reflector and impinging upon the distalreflector is also reflected back. The two reflected beams result inconstructive and destructive interferences that are detected by aphotodetector disposed in console 3.

A variation in strain or temperature changes the optical length ofoptical cavity 11 and sensor 13, and influences the reflectioncharacteristics from which relative deflections of the optical fibersmay be computed. This information in turn permits computation of theforce vector imposed upon distal extremity 5 due to contact with thetissue of the wall of the organ or vessel.

FIG. 6 illustrates a further alternative embodiment of the distalextremity of catheter 1 and contains three Extrinsic Fabry-Perotinterferometer (EFPI) sensors. One of the optical fibers extends beyondthe others and comprises a second EFPI sensor 17 to measure thetemperature of the front end of the distal extremity. An EFPI sensorcomprises optical cavity 11 formed by hollow capillary tube 15 and cutends 16 of the optical fiber. The hollow capillary tube contains air.Operation of the EPFI is similar to that described above for the IFPI,except that the cut ends of the fiber act as the reflectors to reflectspecific wavelengths 18. Light reflected from cut ends 16 result in twobeams that constructively and destructively interfere. A variation instrain or temperature changes the length of the optical cavity andinfluences the reflection characteristics.

FIG. 7 illustrates a further alternative embodiment of the distalextremity of catheter 1, wherein the distal extremity contains threeoptical fibers 7 that form a Michelson interferometer. Each opticalfiber 7 includes reflector 19 at its distal extremity; the fibers arecoupled at their proximal ends by optical coupler 20. A wave is injectedinto fiber 21 from a laser diode disposed in console 3 and is separatedby coupler 20 into each of the optical fibers (“arms”) of theinterferometer. The coupler 20 combines the back reflected light fromeach arm. Using a coherent or low coherence interferometer, variationsin the relative phases of the reflected light from the different fibersare measured to compute the strain experienced by the distal extremityof catheter 1. Based upon the computed strain, the contact force betweenthe distal extremity and the tissue of the organ or vessel wall may bedetermined.

Referring now to FIG. 8, an embodiment wherein the optical fiberscomprise high resolution Brillouin sensors is described. Brillouinsensors use the principle of scattering 22 that is an intrinsicphenomenon of optical fiber. This phenomenon results from theinteraction between the light and the phonons (pressure wave) present inthe fiber. Wave 23 is backscattered with a shift in optical frequencyrelative to the injected wave. One of the optical fibers 7 extendsbeyond the others and comprises a second Brillouin scattering sensor 24to measure the temperature at the front end of the distal extremity. Avariation in strain or temperature changes the shift in opticalfrequency. Using impulsion, phase modulation or other techniques, it ispossible to select different locations 26 along the fiber and to measurethe state of strain at these locations.

Referring to FIGS. 9 and 10, further embodiments of the presentinvention are described that employ intensity-type optical fibersensors. More specifically, FIG. 9 illustrates use of reflectionintensity sensors while FIG. 10 illustrates use of microbendingintensity sensors.

In FIG. 9, reflection intensity sensors comprise connection zones 25within optical fibers 7. Under the effect of a strain caused bydeformation of the distal extremity, or a temperature variation,connection zones 25 modulate the amplitude of the optical wave 26 thatis transmitted and/or reflected. The variation in intensity of thereflected light is measured by apparatus, which is per se known. Anadditional optical fiber also may be provided to perform temperaturemeasurement.

In FIG. 10, microbending intensity sensors comprise connection zones 27disposed along the length of optical fibers 7. Connection zones 27 maybe obtained by introducing microbendings in the fibers. Under the effectof a strain caused by deformation of the distal extremity, or atemperature variation, connection zones 27 modulate the amplitude of theoptical wave 28 that is transmitted and/or reflected. The variation inintensity of the reflected light is measured by apparatus, which is perse known.

According to a preferred embodiment, the three optical fibers may beassembled with each other to form an integral part, as depicted in FIG.11, or embedded with an adhesive or other suitable deformable materialto form cylindrical element 29, as depicted in FIG. 12. This arrangementprovides a very small solid assembly that may in turn be affixed withina lumen of a catheter of otherwise conventional construction, asdepicted in FIG. 13, while also protecting the optical fibers frombreakage. In accordance with the principles of the present invention,bundling the fibers as shown in FIGS. 11-13 ensures that all three ofthe optical fibers are not co-planar.

Referring now to FIGS. 4 and 14, the distal extremity of an exemplaryablation catheter utilizing the load sensing capability of the presentinvention is described. Catheter 1 includes electrodes 30, 31 and 32 andis coupled to front end 33 having irrigation ports 34. Electrodes 30,31, 32, 33 are provided according to the function of the specificapplication for the catheter, for example, endocavity electrocardiogram,radiofrequency ablation, etc. Front end 33 also may be an electrode.Sensor 35 also may be provided that provides three-dimensionalpositioning of the distal extremity of the catheter, with sensor 35being based upon electromagnetic, magnetic, electric, ultrasoundprinciples.

The distal extremity of catheter 1 includes at least three fiber opticsensors 9 configured as described hereinabove. One of the optical fibersextends beyond the others and includes, for example, second Bragggrating 10 that serves as a temperature sensor. Bragg grating 10 isreceived within front end 33 and may be used to compute temperaturechanges in front end 33 resulting from operation of the electrode.Irrigation ports 34 communicate with one or more channels situatedinside the catheter and may be used to deliver a cooling solution, e.g.,saline, to the distal extremity of the catheter during operation of thefront end electrode to lower the temperature of the front end andcontrol the ablation of tissue.

Although front end 33 is illustratively described as configured forperforming radiofrequency ablation, other tissue ablation or treatmentend effectors could be used, such as laser, ultrasound, radiation,microwave and others. Furthermore, other therapeutic means such as theinjector of medication, stem or other types of cells may also besituated in the head of the catheter.

With respect to FIG. 15, a further alternative embodiment is describedwherein a fourth optical fiber is used to measure the temperature of thedistal extremity in the vicinity of the other optical fiber strainsensors. Because the material of the distal extremity of catheter 1 maybe sensitive to temperature variations, a change of temperature of thedistal extremity may result in expansion or contraction of the distalextremity and the embedded optical fibers. This effect may result incomputation of a false force vector. Accordingly, fourth optical fiber 7is slidably disposed in distal extremity 1 so that it is not affected bytemperature induced expansion or contraction of the distal extremity ofthe catheter, and thus provides a reference measurement. If thetemperature of the sensor body is known, however, such as by using afourth optical fiber, thermal expansion or compression of the distalextremity may be compensated in the computation of the force vector.

Referring now to FIG. 16, an alternative embodiment of apparatusutilizing the load sensing system of the present invention is described.Apparatus 40 includes catheter 41 having distal extremity 42 andproximal end 43 coupled to console 45 via cable 44. Construction andoperation of components 41-45 is similar to that described above for theembodiment of FIG. 1.

In accordance with one aspect of the present invention, apparatus 40 ofFIG. 16 further includes robotic control system comprising controller46, input and display device 47 and actuator 48. Actuator 48 is coupledto catheter 41 to manipulate the catheter responsive to commandsgenerated by programmed microprocessor 46. Controller 46 is programmedvia instructions input via input and display device 47, and theoperation of the actuator 48 may be monitored via a display portion thatdevice 47. Controller 46 is coupled to console 45 to receive the outputof the load sensing system of the present invention, and to use thatinformation to control manipulation of catheter 41 and actuator 48.Console 45 also may receive an input from controller 46 that is used todetermine when the end effector of catheter 41 is operated.

For example, catheter 41 may comprise an electrophysiology catheterdesigned to map electrical potentials within a patient's heart. In thiscase, distal extremity 42 may include a series of mapping and ablationelectrodes as described herein above with respect to FIG. 14. Asdescribed above, previously known methods of mapping electricalpotentials within a patient's heart is a time consuming activity,because the clinician determines engagement of with the tissue wall bytactile feedback through the catheter shaft or using impedancemeasurements.

In accordance with the principles of the present invention, actuator 48comprises a multi-axis tool capable of advancing and rotating thecatheter within the patient's heart. Controller 46 may be programmed tomanipulate the catheter until the contact force encountered by distalextremity 42 falls within a predetermined range, as determined viamonitoring by console 45. Once the contact force is determined to fallwithin the predetermined range, the electrical potential may be measuredand recorded. Controller 46 then may reposition the catheter as requiredto map other desired portions of the patient's heart.

Advantageously, because the contact forces applied by the distalextremity can be controlled within desired ranges, the risk of deformingthe tissue wall is reduced. Accordingly, if a three dimensional locatorsystem also is provided in the catheter, such as described above,accurate registration of the measured values and the spatial locationsof the measurement points may be obtained. The load sensing system ofthe present invention similarly may be integrated into a treatmentsystem, for example, including the ablation electrode described abovewith respect to FIG. 14, in which the ablation electrode may beenergized to ablate tissue only when the contact force between thedistal extremity and the tissue wall exceeds a predetermined minimumvalue or falls within a predetermined range.

In addition, where distal extremity 42 of catheter 41 is articulable,controller 46 also may provide a signal to console 45 that adjusts thearticulation of the distal extremity. In this manner, the load sensingsystem of the present invention may be configured not only to serve aspart of a feedback loop to an external controller, but may itself acceptan external control signal that controls operation of an end effector ofthe catheter.

Referring now to FIG. 17, a further alternative embodiment of anablation catheter utilizing the load sensing features of the presentinvention is described. Applicant has observed that some polymersroutinely employed in catheter construction, such as polyethylene have arelatively high coefficient of thermal expansion, and a tendency toabsorb moisture when exposed to bodily fluids.

Although the dimensional changes resulting from moisture absorption andtemperature fluctuations may be small, these environmental factors mayintroduce artifacts into the forces computed by the apparatus. Moreover,the environmental effects may not be entirely removed by use of anadditional optical fiber sensor, such as described with respect to FIG.15. To address the temperature fluctuation issue, a tube having a lowthermal expansion coefficient is disposed in the distal extremity of thecatheter in the vicinity of the sensor portions of the optical fibers.

Referring again to FIG. 17, apparatus 50 comprises catheter 51 havingproximal end 52 coupled via cable 53 to console 54 having processor 55.Apparatus 50 further comprises distal extremity 56 attached to thedistal end of catheter 51 and includes electrode 57 having irrigationports 58 for cooling the tissue during an RF ablation procedure.Proximal end 52, cable 53, console 54, and processor 55 are similar indesign and construction to proximal end 2, cable 4, console 3 andprocessor 6 of the embodiment of FIG. 1, respectively, which aredescribed in detail above. Apparatus 50 differs mainly in theconstruction of distal extremity 56, as described below.

Referring now to FIGS. 18 and 19, subassembly 60 disposed within distalextremity 56 of apparatus 50 is described. Subassembly 60 comprisesirrigation tube 61 coupled at proximal end 52 to an infusion port (notshown) and at distal end 62 to irrigation ports 58 of front end 63.

Front end 63 preferably is metallic and acts as an ablation electrode,and includes irrigation ports 58 in fluid communication with theinterior of irrigation tube 61, so that fluid injected via the infusionport exits through irrigation ports 58.

In FIG. 19, subassembly 60 is disposed within polymeric housing 64,shown partially cut-away for ease of understanding. Optical fibersensors 65 are arranged around the circumference of irrigation tube 61,preferably spaced 120 degrees apart. Sensors 65 are similar in designand construction to optical fiber sensors 7 of the precedingembodiments, and may be configured to measure strain in any appropriatemanner, such as described above and depicted in FIGS. 4-10. Preferably,sensors 65 are Bragg Gratings.

In accordance with one aspect of the invention, irrigation tube 61preferably comprises proximal portion 66 and distal portion 67. Proximalportion 66 preferably comprises a polymer and more preferably comprisesa thin polyimide tube, such as made from Kapton, available from DuPont,and extends from proximal end 52 to within about 1 cm of distal end 62.

Distal portion 67 couples proximal portion 66 to front end 63. Distalportion 67 preferably is electrically conductive, so as to conductelectrical current to front end 63, for example, by wire 59 coupled tothe proximal end of proximal portion 66. Preferably, distal portion 67is formed of a material having a relatively low coefficient of thermalexpansion compared to the rest of catheter 51. Distal portion 67preferably also has a Young's modulus of elasticity such that, whenconfigured as a thin tube, its axial deformation under an applied loadis sufficient to obtain a force resolution with the optical fibersensors 65 of 1 gram. In a preferred embodiment, distal portion 67comprises titanium and has a length of approximately 1 cm, whereas thelength of the measurement regions of optical fibers 65 is about 4 mm.

Referring now to FIGS. 19 and 20, housing 64 is described in greaterdetail. Housing 64 preferably comprises a polymer and extends overdistal portion 67 of irrigation tube 61 to enclose and protect themeasurement regions of optical fiber sensors 65. Housing 64 is bonded todistal portion 67, e.g., with glue or other known attachment means, sothat the distal end of the housing does not contact front end 63, butinstead forms gap 68.

Housing 64 includes central channel 69 configured to receive distalportion 67 of subassembly 60, and may include grooves 70 on the exteriorsurface of the housing 64 to accept wires that electrodes on theexterior of housing 64 to proximal end 52. Housing 64 also includes ribs71 that prevent the housing from directly contacting optical fibersensors 66. Housing 64 further includes stepped diameter region 72 thatfacilitates joining the housing to the proximal portion of catheter 51.

As described above, apparatus 50 may be configured to include thecapability to deflect the distal extremity of catheter 51 using any ofvariety of well-known mechanisms, such as pull-wires. More particularly,referring to FIG. 21, an illustrative embodiment of a deflectablecatheter shaft suitable for use with subassembly 60 of FIGS. 18 and 19is described.

Catheter shaft 80 includes handle 81, elongated shaft 82 and deflectableregion 83. Shaft 82 preferably comprises braided wire tube 84 embeddedwithin biocompatible polymer 85. Deflectable region 83 preferablycomprises flexible catheter material 86 having wire coil 87 embeddedwith it. Pull wire 88 is coupled to anchor ring 89 disposed at distalend 90 of deflectable region 83, and extends through coil spring 91 tohandle 81. Electrical wires 92, irrigation tube 93 (corresponding toirrigation tube 61 in FIG. 18) and the optical fibers (not shown) extendfrom handle 81 through anchor ring 89 to the housing of the distalextremity.

Stepped diameter region 72 of housing 64 engages the distal end ofcatheter shaft 80, so that housing 64 and electrode 57 are disposeddistal to anchor ring 89. In this manner, deflection of deflectableregion 83 does not impact the strains computed by the optical fibersensors used to compute contact forces between the distal extremity ofthe catheter and the wall of the vessel, tissue or organ.

It will be appreciated that other embodiments of an ablation cathetermay employ other features discussed elsewhere in this application. Forexample, an additional sensor may be added to apparatus 50 for measuringtemperature using the above-described principles.

In summary, use of optical fiber strain sensors permits computation of amulti-dimensional force vector that arises during contact of the distalextremity of the catheter with the wall of the tissue, organ or vessel.When such information is combined with a 3D positioning sensor, precisemapping may be obtained to permit diagnosis or treatment of tissue at anoptimal applied force. The small size of the optical fiber strainsensors and high resolution of measurements obtained by these devicesallows highly precise measurements to be obtained even in environmentsthat are humid and subject to electromagnetic interference.

While preferred illustrative embodiments of the invention are describedabove, it will be apparent to one skilled in the art that variouschanges and modifications may be made therein without departing from theinvention. The appended claims are intended to cover all such changesand modifications that fall within the true spirit and scope of theinvention.

The invention claimed is:
 1. A method to determine a force, comprising:receiving a plurality of signals from a plurality of sensors located ata distal end of a catheter; determining a temperature of the distal endof the catheter by changes in the plurality of signals received from theplurality of sensors; processing the plurality of signals to determine aforce vector applied to the distal end of the catheter; outputting asignal indicative of the force vector.
 2. The method according to claim1, wherein the force vector is a three-dimensional force vector.
 3. Themethod according to claim 1, wherein the plurality of signals comprisesthree signals and wherein the plurality of sensors comprises threesensors.
 4. The method according to claim 1, further comprisingreceiving specific information pertaining to the catheter.
 5. The methodaccording to claim 4, wherein the specific information comprisescalibration information acquired during a calibration step and stored ina memory of the catheter.
 6. The method according to claim 5, whereinthe calibration information comprises a force conversion matrix.
 7. Themethod according to claim 1, wherein the force vector comprises a normalforce, a transverse force, and an angle of application of the transverseforce.
 8. The method according to claim 1, wherein outputting a signalcomprises outputting a graphic including a representation of a magnitudeand a direction of a transverse force applied to the distal end of thecatheter.
 9. The method according to claim 1, wherein determining atemperature of the distal end of the catheter comprises determiningmultiple temperatures.
 10. The method according to claim 1, whereinprocessing the plurality of signals further comprises accounting forchanges in temperature at the distal end of the catheter.
 11. The methodaccording to claim 1, wherein processing the plurality of signalscomprises a continuous process and outputting a signal comprises acontinuous process such that the outputted signal of the force vectorapplied to the distal end of the catheter can be used to guide orcontrol a use of the catheter.
 12. A system for determining a force,comprising: a console comprising a processing logic, wherein the consoleis configured to couple to a catheter and to receive an output of atleast two sensors, wherein the processing logic is configured todetermine a temperature of the distal end of the catheter by trackingchanges in the output received from the at least two sensors, whereinthe processing logic is configured to determine a force vector from theoutput of the at least two sensors, and wherein the console isconfigured to output a signal indicative of the force vector.
 13. Thesystem according to claim 12, wherein the processing logic is configuredto determine a three-dimensional force vector.
 14. The system accordingto claim 12, wherein the at least two sensors comprises three sensors.15. The system according to claim 12, wherein the console is furtherconfigured to receive specific information pertaining to the catheter.16. The system according to claim 15, wherein the specific informationcomprises calibration information acquired during a calibration step andstored in a memory of the catheter.
 17. The system according to claim12, wherein the force vector comprises a normal force, a transverseforce, and an angle of application of the transverse force.
 18. Thesystem according to claim 12, wherein the outputted signal comprises agraphic including a representation of a magnitude and a direction of atransverse force applied to the distal end of the catheter.
 19. Thesystem according to claim 12, wherein the processing logic is furtherconfigured to determine a plurality of temperatures of the distal end ofthe catheter.
 20. The system according to claim 12, wherein theprocessing logic is further configured to account for changes intemperature at the distal end of the catheter by tracking changes in theoutput received from the at least two sensors.